The invention is particularly used for the gripping of textile sheets, but can also be used for other sheet materials which allow the penetration or pointed tips into the surface structure, the tips serving for the removal of the respective top sheet or layer from the stack, as well as for the secure holding of the sheet during transport within the production process.
Methods and apparatus for the separating of textile sheets from a stack are known, in which needle-like gripping devices penetrate the material, grip the top material layer and remove it. Various constructions of needle gripping devices have been developed. There are, for example, apparatus, which grip the top layer with needle-like elements, pointing in an obliquely outward direction, penetrating the material, and with the material being subsequently stretched because of the expansion of these elements. The danger of damage to the material is considerable, since in order to securely grip the material layer, sufficient force has to be present to spread the needles.
Another method introduces needles, directed opposite to one another, into the material in such a way that they cross over inside the material, thus allowing a punctiform gripping of the top material layer. These types of apparatus require high production and monitoring costs, since their functioning depends on the accuracy of the depth of penetration of the needles, as compared to the strength or thickness of the material.
In an additional group of methods, the top layer of a stack of textile sheets is lifted, with gripping devices pushing the material into a fold by their gripping movements, and in this manner gripping the material. Apparatus configurations are known, which differ from each other in the way by which they push the material together to a fold. The folding, which is typical for this method, has the disadvantage that the displacement of the top layer of material which is, necessary for the fold formation, requires the overcoming of frictional forces along the mating surfaces of the material layer to be gripped, and the material layer underneath it. An improvement of the attachment between the contoured bottom sides of the gripping device and the upper side of the top material layer, by increasing the attachment power of the gripping apparatus, is successful only in the case of smooth materials, however, this increases the probability that several layers will be gripped at the same time.